1. Field of the Invention
This disclosure relates to a position indicator used with a position detecting sensor.
2. Description of the Related Art
The following position indicator has been provided as a position indicator used with a position detecting sensor in which position detection is performed. Specifically, the position indicator has a configuration of so-called full-duplex communication, in which a signal input channel and a signal output channel independently exist, and thereby has a high affinity with the position detecting sensor. Furthermore, the position indicator has high general versatility and can ensure predetermined waveform correlativity between an input signal and an output signal (refer to Japanese Patent No. 4683505 (Patent Document 1)).
FIG. 10 is a diagram for explaining the conceptual configuration of a position indicator 301 of this Patent Document 1 and the processing operation thereof in a generalizing manner and shows a state in which the position indicator 301 is located over a plate surface of a capacitive position detecting sensor 302.
In the position indicator 301, a signal processing circuit 304 and a battery 305 that provides a supply voltage to the signal processing circuit 304 are housed in a hollow part of a tubular chassis 303 that has an opening on one end in the axial center direction and is formed into a pen shape. The chassis 303 is formed by covering at least a part which an operator holds this position indicator in the outer circumferential surface of a tubular body formed of, e.g., an insulating material such as a synthetic resin by, e.g., an electrical conductor such as a metal.
As shown in a partially enlarged view of FIG. 11, the opening side of the chassis 303 of this position indicator 301 is formed as a tapered part 303a that gradually becomes thinner toward the tip, and a peripheral electrode 306 that is formed into a ring shape and is formed of a metal having electrical conductivity is attached to the outer circumferential side of the tapered part 303a. Furthermore, a central electrode 307 is housed in the hollow part of the chassis 303 of the position indicator 301 in a state in which a tip part 307a of the central electrode 307 protrudes from the opening to the outside as shown in FIG. 11. The tip of the central electrode 307 is covered by an elastic protective member 307b formed of electrically-conductive elastic rubber or the like so that an indication input surface of the position detecting sensor 302 may be prevented from being scratched and a contact area with the indication input surface may be made larger.
In this case, in the direction orthogonal to the axial center direction of the position indicator 301, the tapered part 303a of the chassis 303 intervenes between the peripheral electrode 306 and the central electrode 307. The peripheral electrode 306 and the central electrode 307 are insulated from each other by this tapered part 303a of the chassis 303. Moreover, in the direction orthogonal to the axial center direction of the position indicator 301, a shield member 308 for effectively preventing electrical interference between the peripheral electrode 306 and the central electrode 307 is provided between the peripheral electrode 306 and the central electrode 307. The shield member 308 is formed of a tubular conductor composed of an electrically-conductive metal 308a having an insulating layer 308b formed on the inner wall surface, and the central electrode 307 is housed in this tubular conductor. Therefore, the central electrode 307 is configured to be surrounded by the shield member 308 and the shield member is connected to the ground (earth: the same hereinafter) to make a capacitive shield.
When this position indicator 301 is disposed over the position detecting sensor 302, as shown in FIG. 10, the peripheral electrode 306 is coupled to the position detecting sensor 302 via capacitance C1 and the central electrode 307 is also coupled to the position detecting sensor 302 via capacitance C2.
Meanwhile, an alternating current (AC) signal flows in the position detecting sensor 302 and thus this AC signal is supplied as a current signal to the signal processing circuit 304 via the capacitance C1 and the peripheral electrode 306. This signal processing circuit 304 executes processing of intensifying a signal, such as amplifying an input AC signal, and supplies an AC signal that is an output signal of the signal processing result to the central electrode 307. When the position indicator 301 exists over the position detecting sensor 302, the central electrode 307 is coupled to the position detecting sensor 302 via the capacitance C2 and thus the AC signal is returned from the position indicator 301 to the position detecting sensor 302.
Because the intensified AC signal is returned from the position indicator 301 to the position detecting sensor 302 in the above manner, the position detecting sensor 302 can detect the position indicated by the position indicator 301 with high sensitivity.
In this case, when the voltage of the AC signal of the position detecting sensor 302 in the transmitting conductor is defined as V and the voltage of the central electrode 307 of the position indicator 301 is defined as e and capacitance between the peripheral electrode 306 and the central electrode 307 is defined as C3 (see FIG. 10), a relationship ofe≦C1/C3·V is satisfied. Therefore, to increase the voltage e of the central electrode 307, it is advantageous that the capacitance C3 between the peripheral electrode 306 and the central electrode 307 is as low as possible.
In the position indicator 301, the capacitance C3 between the peripheral electrode 306 and the central electrode 307 is made low by interposing the shield member 308 between the peripheral electrode 306 and the central electrode 307 to make the coupling between them as small as possible. This can increase the voltage e and efficiently enhance the sensitivity.
As described in Patent Document 1, it is also possible for the position indicator 301 to be configured to receive the AC signal from the position detecting sensor 302 by the central electrode 307 and transmit the AC signal resulting from the signal intensification by the signal processing circuit 304 from the peripheral electrode 306.
Recently, along with an increase in the preciseness of the indicated position in the position detecting sensor, demands for reduction in the thickness of the core body (central electrode) of the position indicator and hence for reduction in the thickness of the position indicator are increasing.
However, in the position indicator 301 of the above-described Patent Document 1, an insulating part (tapered part 303a of the chassis 303), a shield part (shield member 308), and an insulating part (insulating layer 308a) need to be provided between the central electrode 307 and the peripheral electrode 306 and it is difficult to satisfy the demands for the thickness reduction.
Furthermore, if a writing pressure being applied to the position indicator can be detected in the position detecting sensor, e.g., processing of changing the line width in line drawing by a user with use of the position indicator according to the writing pressure can be executed, which is convenient. Therefore, it is desirable for the position indicator to be configured to include a writing pressure detecting measure that detects the writing pressure applied to the core body (central electrode) and transmit writing pressure information detected by this writing pressure detecting measure to the position detecting sensor.
To detect the writing pressure by such a writing pressure detecting measure, the writing pressure applied to the core body (central electrode) of the position indicator needs to be transmitted to the writing pressure detecting measure. For this purpose, a configuration for allowing the core body (central electrode) of the position indicator to move in the axial center direction of the position indicator and surely transmitting the writing pressure is necessary.
In this case, the position indicator needs to have a configuration to ensure a predetermined thickness as the thickness of the core body in order to surely transmit the writing pressure and allow the central electrode to move in the axial center direction of the position indicator while having a structure to make the coupling between the peripheral electrode 306 and the central electrode 307 as small as possible. Thus, it is more difficult to employ the configuration designed in consideration of thickness reduction.